This unusual amino acid is used in Solid Phase Peptide Synthesis (SPPS) for the synthesis of modifiable side-chain peptides and proteins.1 The side-chain azido (N3) group is stable in trifluoroacetic acid (TFA) and piperidine (Pip), two reagents commonly used in SPPS. The azido group can be readily converted to an amine on the solid phase or in solution via Staudinger reduction.2 In addition, incorporation of azidohomoalanine into proteins has shown promise as an effective IR probe of local electrostatic environments in proteins.3